Ballast water refers to sea water that is charged into a ballast tank of a vessel to maintain balance of the vessel when the vessel sails without cargo.
As marine transportation rates have gradually increased along with an increase in international trade, the number of vessels used has increased, and the vessels used are becoming larger. As a result, the amount of ballast water used in vessels has greatly increased. As the amount of ballast water used in vessels is increased, occurrence of damage to indigenous ocean ecosystems attributable to the introduction of foreign marine creature species is also increased. To solve such international environmental issues, in 2004, the IMO (International Maritime Organization) established ‘International Convention for the Control and Management for ships’ Ballast Water and Sediments’. Since 2009, ballast water treatment apparatuses have been obligatorily installed in newly constructed vessels.
Of apparatuses for treating ballast water, ultraviolet ballast water treatment apparatuses that sterilize ballast water using ultraviolet rays are widely used. FIG. 1 is an exploded perspective view of a conventional ultraviolet ballast water treatment apparatus. FIG. 2 is a sectional view of the conventional ultraviolet ballast water treatment apparatus.
Referring to FIGS. 1 and 2, the conventional ultraviolet ballast water treatment apparatus includes a cylindrical body 1001. Due to the cylindrical shape of the body 1001, ultraviolet lamps 1002 provided in the body 1001 are also arranged in a circumferential shape corresponding to the cylindrical shape of the body 1001. As shown in FIG. 2, when the number of ultraviolet lamps 1002 is comparatively large, the ultraviolet lamps 1002 are arranged in a plurality of rows having different diameters.
However, in the conventional ultraviolet ballast water treatment apparatus, because the ultraviolet lamps 1002 must be densely arranged at regular intervals in the body 1001 having a circular cross-section, the number of ultraviolet lamps per a unit cross-sectional area is increased, and the power consumption is thus increased. When it is intended to increase the number of ultraviolet lamps and thus increase the ballast water treatment capacity, a circumferential row must be added. Therefore, the cross-sectional area of the body 1001 is greatly increased by the square of an increased radius (the area of a circle=πr2). In addition, the number of ultraviolet lamps of the added circumferential row must be greater than that of the existing outermost row (the circumference of the added circumferential row is larger than that of the existing outermost row). As such, it is impossible to increase the capacity scale of ballast water treatment by a small degree. Thus, it is difficult to increase the treatment capacity by only the required degree.
Moreover, as shown in FIG. 2, when the ultraviolet lamps 1002 are arranged in a circumferential direction, there is the possibility of ballast water linearly passing between the ultraviolet lamps 1002 without making direct contact with the ultraviolet lamps 1002 while passing through the ultraviolet ballast water treatment apparatus (refer to the arrows designated by {circle around (a)}, {circle around (b)}, and {circle around (c)}). Given the fact that the treatment effect using ultraviolet rays is proportional not only to the intensity of ultraviolet rays but also the time for which ultraviolet rays are applied to ballast water, the ballast water treatment effect of the conventional technique is largely reduced because the speed of the flow of ballast water (refer to {circle around (a)}, {circle around (b)}, and {circle around (c)}) that linearly flows without making contact with any ultraviolet lamp 1002 is increased and thus the time for which ultraviolet rays are applied to ballast water is reduced.